A micro-electromechanical system (MEMS) is a microscopic machine that is fabricated using the same types of steps (e.g., the deposition of layers of material and the selective removal of the layers of material) that are used to fabricate conventional analog and digital CMOS circuits.
One type of MEMS is a microphone. A capacitive MEMS microphone uses a membrane (or diaphragm) that vibrates in response to pressure changes (e.g., sound waves). The membrane is a thin layer of material suspended across an opening in a substrate. The microphone converts the pressure changes into electrical signals by measuring changes in the deformation of the membrane. The deformation of the membrane, in turn, leads to changes in the capacitance of the membrane (as part of a capacitive membrane/counter electrode arrangement). In operation, changes in air pressure (e.g., sound waves) cause the membrane to vibrate which, in turn, causes changes in the capacitance of the membrane that are proportional to the deformation of the membrane, and thus can be used to convert pressure waves into electrical signals.
MEMS microphones are susceptible to the influence of mechanical vibrations (e.g., structure-borne sound), such as may relate to movement of the microphone and/or the device in which the microphone is employed. These vibrations can be undesirably detected as noise, and interfere with the ability of the microphone to accurately detect sound. In addition, many approaches to mitigating noise can affect the ability of the microphone to detect sound, hindering the resolution of the microphone.
The implementation of MEMS microphones continues to be challenging, in view of the above and other issues.